As is known in the art, Electronic Throttle Control (ETC) offers many benefits in delivering an accurate airflow requested by the driver via accelerator pedal interaction. Matching the driver requested airflow during both steady-state and transient operation helps to give the driver a sense of a direct connection with the vehicle.
More particularly, when there is a disturbance in the system to affect airflow or a transient desiring more airflow, normally, one opens the throttle to the appropriate setting and then has to wait a few cycles for the manifold to fill up. This produces an undesirable delay to the driver. A technique for reducing the delay due to manifold filling is discussed in U.S. Pat. No. 6,219,611. In this patent it is described to move outlet flow control devices, such as variable cam position mechanisms, in order to achieve a quicker manifold filling response to a step change in throttle area or angle at the inlet to the manifold. While this method is effective at decreasing manifold filling delays, it can have the potential to degrade fuel economy and emissions by placing outlet control devices, such as variable cam timing mechanisms, in transient positions.
Now that there are electronically controlled throttles, what can be done is to swing the throttle valve open farther than the steady state position and to load the system with air. Then, the throttle valve reverts back to where it needs to be to satisfy driver demand once the manifold filling transient condition is completed. A method to do this in relation to a variable cam timing (VCT) transition is discussed in U.S. Pat. No. 5,690,071. This patent describes a mechanism for cancelling out disturbances in manifold outlet flow by means of the electronic throttle, however it requires a relatively high computational load on the powertrain control module (PCM) or engine control unit (ECU).
As is also known in the art, many ETC systems employ a control method called “Pedal Follower”, in which a pedal movement directly translates to a requested throttle position. This method allows for a square-edged response in throttle position for a square edged input to the pedal. Another major ETC system is known as “Torque Based”, in which a pedal movement is translated to a desired torque (either indicated torque or brake torque at a potential variety of points in the powertrain: engine flywheel, transmission output shaft, or at the wheels). The end result is a desired cylinder airflow, which is then scheduled via the throttle. Many existing systems directly schedule the throttle to achieve the steady-state cylinder flow that is desired. This provides for stable scheduling, but sacrifices transient response, as manifold filling lag occurs between the time that the throttle is placed in the steady-state flow position and the time when the steady-state flow is achieved.
One known method for compensating for transient inaccuracy is to use closed-loop feedback on a sensor which gives information as to the state of the manifold, such as a mass air-flow sensor or manifold absolute pressure sensor. This method certainly can give very reasonable delivery of the desired cylinder flow during transient airflow requests; however, in the closed loop compensation method the fact that closed-loop control method uses feedback will always have a delay in air-mass matching. Also, sensors used in the feedback control can experience drift, noise, and failure which can cause undesirable throttle control under these conditions.